This invention pertains generally to a gearshift for use on a dual derailleur type of multi-speed bicycle, more particularly to a gearshift of such type wherein a unitary structure provides manually operable actuator means accessible for controlling the bicycle's front and rear derailleurs, still more particularly to such a gearshift having a single actuator for either independently or simultaneously controlling both the front and rear derailleurs, specifically to the provision of such a gearshift having said single actuator pivotally centered on perpendicular first and second axes for a uniform mode of manipulation about both axes, to the provision of embodiments of such gearshift which may be applied to or retrofitted on any configuration of dual derailleur bicycle, and to the provision of at least one embodiment of such gearshift wherein said single actuator is manipulable while maintaining a hold on both ends of the bicycle's handlebar.
A dual derailleur bicycle is one having multiple front sprockets (typically two or three) of different pitch diameter mounted on the bicycle's pedal crank axis, multiple rear sprockets (typically five, six or seven) of different pitch diameter mounted on the bicycle's rear wheel axis and a roller chain forming a closed loop about one each of said front and rear sprockets. Different gear ratios are effected between the pedal crank and rear wheel axes for greater speed or easier pedaling depending upon which one of the front and rear sprockets are connected together by the roller chain. The roller chain is transferred from one to another of the front and rear sprockets by front and rear derailleur devices which are mounted on the bicycle adjacent the front and rear sprockets, respectively. The front derailleur, when moved alternately in opposite directions axially of the pedal crank axis, derails the roller chain from one front sprocket and positions it upon another, and the rear derailleur, when moved alternately in opposite directions axially of the rear wheel axis, derails the roller chain from one rear sprocket and positions it upon another. The. derailleurs are caused to move from one sprocket alignment position to another by linear movement of a pair of cables which are connected at one end to the derailleurs and which extend from same to a gearshift device which the rider operates to effect said linear movement of the cables.
A conventional gearshift provides two actuators, originally levers, more recently twistgrips, one for linearly positioning the cable leading to the front derailleur and the other for linearly positioning the cable leading to the rear derailleur. Depending upon the direction of movement of the two actuators the cables are caused to either pull the derailleurs from one sprocket alignment position to another or allow spring biases incorporated in the derailleurs to return the derailleurs to a previous sprocket alignment position.
The prior art provides such gearshift means in several configurations. In earliest configuration the gearshift is a unitary structure having two levers pivotally secured to and positioned upright on a common support bracket that is attached to the bicycle's frame or on the stem that supports the bicycle's handlebar. If mounted on the frame, the frame is equipped with pulley wheels or fixed guides which route the cables from the gearshift to the derailleurs. If mounted on the handlebar stem at least a portion of each cable extending from the gearshift to the bicycle's frame is enclosed in a flexible tubular casing which enables linear movement of the cables in an arcuate path in order that the bicycle can be steered; the casings having their ends stopped to prevent linear movement of the casings while permitting linear movement of the contained cables.
All such frame or stem mounted gearshifts have required the rider to release his grasp of one handgrip or the other in order to manipulate the lever which is positioned on one side or the other of the bicycle's frame or handlebar stem, as the case may be.
In order to improve safety and increase convenience in a later configuration the gearshift has comprised two distinct structures each carrying one lever; i.e., the system comprises two single-lever gearshift devices, one for controlling the front derailleur and the other for controlling the rear derailleur, which are mounted as close as possible to the handgrips for operation using the hand nearest each gearshift device while maintaining a grasp of both handgrips.
In one arrangement the support brackets of the two gearshifts are inserted into the ends of the tubular handlebar with the levers projecting outboard of the handgrips and the rider lifts or lowers the levers using his fingers or palms while a portion of his palms remains on the handgrips.
In another arrangement the support brackets of the two gearshifts are clamped on top of the handlebar inboard of and as close as possible to the handgrips. In this configuration the levers have been positioned on their sides for pivoting about vertical axes and the rider manipulates them with his thumbs while substantially maintaining his grasp of both handgrips. This arrangement has proven to be less than wholly satisfactory because it strains the hands to operate the levers while still holding onto the handgrips and the rider finds himself releasing a handgrip to operate an adjacent lever.
A recent improvement in such "two gearshift" configurations substitutes twistgrips for the levers. The twistgrips are cylindrical members concentrically rotatable about the longitudinal axis of straight end portions of a bicycle handlebar and are axially positioned on same inboard of and as close as possible to the handgrips conventionally provided on the handlebar and which remain stationary on the ends of the handlebar. The derailleur cables are connected to the twistgrips such that rotation of the twistgrips about the handlebar effects linear movement of the derailleur cables. To operate either twistgrip the rider wraps his hand around the twistgrip and rotates it one way or the other about the longitudinal axis of the handlebar while a portion of his palm overlies and rotates about the handgrip, ready to grasp it tightly should the need arise. The clamp fastening standard brake levers tends to interfere with such mode of operation because the relatively short levers require securing the clamps immediately adjacent the handgrips. More comfortable operation of such twistgrip gearshifts requires a specially designed brake lever that permits its clamp to be located further inboard from the handgrip so that a space is provided between such clamp and the handgrip for mounting a twistgrip gearshift immediately adjacent to the handgrip.
Although favored over prior concepts it is clear that the twistgrip gearshift has its limitations, including a diminished grasp of the handgrip during rotation of the twistgrip.
Of course a continuing limitation of all the above described configurations is that the rider must still operate two actuators to obtain a single result where simultaneous operation of both derailleurs is required.
It is not always obvious which actuator is to be repositioned or whether both actuators are to be repositioned simultaneously in order to effect a given desired gear ratio. Many riders find it inconvenient and awkward having to manipulate two actuators in order to obtain a single result and experience difficulty in quickly obtaining the required combination of front and rear sprockets; e.g., for instantly shifting from highest to lower gear when stopping for easy startup and when suddenly confronted by a hill. Accordingly, a more convenient means has long been desired.
U.S. Pat. No. 3,808,907 to Yamaguchi discloses a gearshift for a dual derailleur bicycle wherein the gearshift has a single lever that is pivotable about a first axis for controlling one derailleur and is also pivotable about a second axis perpendicular to the first axis for controlling the other derailleur, but does not provide such lever centered on both axes of its pivotal movement. Instead, in each of five embodiments, although the lower end portion of Yamaguchi's lever is pivotally secured for rotation about a first axis so that only the upper end of the lever pivots uniformly about the first axis as shown in Yamaguchi's FIG. 3 for control of one derailleur cable, as recited in each of four claims, for control of the other derailleur cable the lever is "oscillatable on a pivot extending radially from" either a drum or a bevel gear that defines the second axis of the lever's pivotal movability, such drum or bevel gear holding the lever as a whole including its lower end portion positioned a substantial distance away from the second axis, with the undesirable result that the whole body of the lever must be moved arcuately about the second axis, whereby, instead of only the upper end of the lever comfortably pivoting from a centered position on the second axis, the operator experiences an awkward up and down movement of the lever as shown in Yamaguchi's FIG. 4.
Yamaguchi's gearshift is further limited by unnecessary complexity and therefore added cost and excessive weight as well as bulkiness requiring more space on a bicycle, all of which critically limit the practical usefulness of Yamaguchi's gearshift.
The present improvement provides a single actuator gearshift having its actuator centered on both the first and second axes of its pivotal movability so that the actuator pivots in a comfortable and uniform manner for control of either derailleur, and which is characterized by fewness of parts, lowest cost, compactness, light weight, and also, compatibility with any configuration of dual derailleur bicycle. A handlebar mounted embodiment adds the safety and convenience afforded by the twistgrip type of gearshift with the added advantage of a single actuator mode of operation for instant and easily learned shifting through all the gears.